Dental caries (tooth decay) is one of the most prevalent and costly infectious diseases in the United States. Oral cavity harbors a complex microbial community consisting of over 600 different non-harmful/commensal microbial species together with a limited number of acid- producing (cariogenic) bacteria such as Streptococcus mutans and Lactobacillus species. The acids generated by these pathogenic bacteria are a key virulence factor that causes the demineralization of tooth structure and inhibits the growth of non-pathogenic commensal bacteria within the same microbial community. Eliminating the majority of acid-producing bacteria would be an effective way to treat and prevent tooth decay. The current anti-microbial strategies used to treat dental caries consist primarily of mechanical removal of dental plaque or a generalized killing of oral bacteria with broad-spectrum anti-microbial compounds. These "remove all, kill-all" approaches have shown limited efficacy, since a "cleaned" tooth surface provides an equal opportunity for commensal as well as pathogenic bacteria to re-colonize in the non-sterile environment of the oral cavity. Cariogenic bacteria can dominate the dental plaque after the treatment and start another cycle of cariogenesis. In this study, we propose a novel approach to address this problem. Our working hypothesis is that by selectively killing or inhibiting the acid-producing bacteria within a pathogenic dental plaque, we can establish a non- pathologic, commensal microbial community. This "healthy plaque" will then serve as an effective barrier to prevent subsequent re-colonization of cariogenic bacteria on the tooth's surfaces, leading to a sustained anti-caries effect. To achieve this goal, we propose to create and perfect a novel set of acid-activated antimicrobial peptides that will only exhibit antimicrobial activity against acid-producing bacteria through activation by the local low pH environment created by these bacteria. In phase I, we will obtain solid preliminary data to establish the technical/scientific merit of this novel approach. The specific goals are: " Aim 1. Based on the fact that histidine residues within antimicrobial peptides can provide charged groups in a pH dependent manner, we will design, synthesize and test a series of small peptides for their acid-activated antimicrobial activities. " Aim 2. For the peptides with pH activated antimicrobial activities, we will test their targeted killing ability against different acid-producing bacteria (such as S. mutans) within multispecies in vitro dental biofilms. Furthermore, we will validate the working hypothesis by examining whether these novel peptides can trigger a community shift towards a "healthy plaque", which can prevent the future colonization or overgrowth of cariogenic bacteria. The Phase-II studies aim to optimize, improve and perfect these promising molecules into actual therapeutic products against oral microbial infections. The successful execution of this research plan will lead to the development of a targeted antimicrobial therapy against cariogenic bacteria. Phase III follow up works will include human clinical trials to evaluate the safety and efficacy of these STAMP-based therapeutic agents. PUBLIC HEALTH RELEVANCE: The direct outcome of this study will be to provide novel targeted antimicrobial therapy against dental caries, which is one of the most prevalent and costly infectious diseases in the United States. The technology developed in this study could significantly reduce or even eliminate dental caries, dramatically reducing the human suffering and high costs associated with the disease. They will be low cost and have long lasting effects, which is particularly suitable for underserved populations. The goal of this study is consistent with the mission of the SBIR program. It will encourage and support research from small businesses on the etiology, pathogenesis, prevention, diagnosis, and treatment of oral, craniofacial, and dental diseases and disorders.